1. Field of the Invention
The present invention relates to an image forming apparatus that is mounted in a laser printer, copying machine or the like, as well as to an image forming method, and more particularly, to a high-speed image forming apparatus and an image forming method applied in a high-speed apparatus.
2. Description of the Related Art
According to the conventional art, in an image forming apparatus such as a laser printer, a laser beam that is emitted toward the scanned member is switched ON or OFF based on a pulse output by a pulse width modulation unit, because a pulse width modulation unit can control the width of the laser beam for one dot based on the width of the output pulse, thereby enabling gradation imaging. The pulse width modulation unit receives input of image data, and outputs a pulse in synchronization with an output pixel clock signal, which is an operation clock signal for the image output section. In such a laser printer, the resolution in the main scanning direction is determined based on the number of dots in a line. The number of printed dots corresponds to the number of times the laser beam is turned ON and OFF by the pulse width modulation unit. In other words, the number of dots in a line corresponds to the number of output pixel clock signals for a line. Accordingly, the resolution in the main scanning direction depends on the frequency of the output pixel clock signal.
In the conventional image forming apparatus described above, in order to increase the resolution in the main scanning direction, the frequency of the output pixel clock signal should be increased. However, if the frequency of the output pixel clock signal is increased, the operation frequency for the image processing section that generate image data to be input to the pulse width modulation unit must be increased as well, or else the generation of image data would not keep up with the image output. This makes it very difficult for high-speed apparatuses that already carry out processing at a speed near the maximum operation speed of the image processing section to further increase the resolution.